But now Steyer is pursuing an aggressive financial campaign to support Democratic candidates and push climate change measures on both the federal and state level, sometimes by using stinging attack ads. He is backing his NextGen Climate Action group with $50 million and hoping to raise another $50 million from donors. That would make it one of the biggest outside political groups in the country.

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Now, Steyer’s political activities have made him a target of Republicans and conservative groups that increasingly view Steyer as the liberal version of the billionaire Koch brothers. The Koch brothers have been vilified by Democrats for their enormous financial support of Republican candidates and conservative causes. On the surface, it appears conservatives have found their own billionaire punching bag.

Steyer has been targeted by American Commitment, a GOP-leaning group that has started a campaign to link Democratic candidates to Steyer. It recently started running an online ad that claims Steyer is to blame for the Obama administration dragging its feet on making a decision on the Keystone pipeline. The purpose of the ad is to accuse Democratic Senator Mark Udall, who is running for re-election in Colorado, of being in the pocket of Steyer and his environmental agenda. American Commitment previously ran an online ad called “Steyer Infection,” saying he was one of Senate Majority Leader Harry Reid’s “billionaire buddies” and was blocking energy opportunities in America even though his hedge fund once financed Indonesia’s second biggest coal company.

Jennifer Rubin, a conservative blogger at The Washington Post, took the baton on Wednesday and called Steyer a “self-deluded liberal billionaire,” reacting to comments Steyer made to Politico and The Washington Post, in which Steyer said “there are real distinctions between the Koch brothers and us.” Steyer said that the Kochs’ political efforts “line up perfectly with their pocketbooks—and that’s not true for us,” a notion that Rubin wrote “boils down to typical left-wing arrogance.”

Meanwhile, the conservative Washington Free-Beacon has been running articles that are critical of how Steyer ran Farallon. One article focused on the work of UnFarallon, a student group that a decade ago championed the idea of universities disclosing their private equity investments. The group made a big deal of Farallon’s 1995 partnership with Yale that invested in a water-development project in Colorado that the group said was bad for the environment. Steyer and Farallon have always claimed that the allegations were misguided and the project never went forward (the land was eventually sold and became a national park). But Steyer was clearly uncomfortable a decade ago being singled out for public attack. This election cycle there is a much bigger bullseye on his back.

The conservative press has followed up with accusations that Steyer had ties to an alleged $67 million Ponzi scheme, referring to a lawsuit in Texas that centers around German real estate investors. Farallon has denied wrongdoing, saying it was only marginally involved in the project and noting that the judge overseeing the case dismissed the firm from the lawsuit.

The campaign against Steyer is reminiscent of President Barack Obama’s attack ads against Mitt Romney’s private equity background during the 2012 presidential campaign. In such a scenario, Farallon might become the Bain Capital of the 2014 election cycle. Bain Capital, the large private equity firm founded by Romney, was vilified throughout 2012 in a massive media campaign designed to undermine Romney. Steyer left Farallon in 2012 and the San Francisco-based firm, which oversees some $19 billion, is now run by Andrew Spokes.